In a storage phosphor imaging system as described in U.S. Pat. No. Re. 31,847, reissued Mar. 12, 1985, to Luckey, a storage phosphor is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a helium neon gas laser or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wavelength, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by a photodetector, such as a photomultiplier, to produce an electronic image signal. Typically the storage phosphor is translated in a page scan direction past the laser beam which is repeatedly deflected in a line scan direction perpendicular to the page scan motion of the storage phosphor to form a scanning raster pattern of a matrix of pixels.
Typically, storage phosphors of different sizes and different x-ray exposure speeds are used in a diagnostic x-ray facility. Thus, different storage phosphor sizes are used in the x-ray exposure of different body parts, e.g., a larger size storage phosphor is needed for a chest x-ray than for a breast x-ray. Similarly, storage phosphors of different x-ray exposure speeds are used, for different diagnostic applications. Where different size storage phosphors are scanned, the scanning raster pattern size and scanning beam size may change. Such changes result in changing levels of emitted light which must be compensated either in reading the storage phosphor and/or in processing the read x-ray image signal. If the storage phosphor size and speed are encoded in a scanning type bar code associated with the storage phosphor, scanning such a bar code while the storage phosphor is moving can result in undesirable artifacts and reliability problems due to storage phosphor vibration. Such artifacts and reliability problems can result in improper reading and processing of an x-ray image signal. Moreover, bar code scanning devices are very expensive.
There is thus a problem in storage phosphor imaging systems of providing apparatus for detecting storage phosphor parameters such as size and exposure speed which is cost effective, reliable and artifact free.